Ultrasonic transducer systems are finding increasing applications in such fields as material testing, product testing and analysis, medical diagnosis, and other medical functions. Such systems, particularly when used for medical diagnosis, may provide image data which is displayed on a cathode ray tube or other suitable display to provide dynamic images of the heart, lungs, or other internal organs, and may also be operated in a Doppler or color-flow mode to indicate the direction and velocity of flow at a particular point of blood or other selected bodily fluid. With the latter type of data, the image appearing on the display may, for example, be in one color when the blood or other fluid is flowing in one direction, and in a contrasting color when the blood or fluid is flowing in the opposite direction. The intensity of the color indicates the rate of fluid flow in the indicated direction at the point. Many systems, particularly in the medical field, are adapted to simultaneously provide both image and color flow data. An example of such a system is the Hewlett Packard Ultrasonic Scanner Model No. 77020AC revision K.
In such systems, while a single scan line is adequate to obtain the data necessary for an image of the points being scanned on the line to be displayed, a packet of lines, for example from four to sixteen scan lines, may be required to provide the data necessary to produce a Doppler color flow image of blood or other fluid flow at the point. The large number of scan lines required to scan a target such as the heart to obtain color flow data indicative of blood flow at valves or other points therein, significantly reduces the frame rate at which such scans can be performed. This may cause an image distorting flicker of the resulting display. Reducing the number of scan lines reduces the ability of the system to determine and indicate flow rate and thus makes the data provided by the system less accurate and less useful. A need therefore exists for a relatively simple and inexpensive means of improving the frame rate of an ultrasonic transducer system of the type providing a Doppler color-flow display without reducing the number of scan lines in the packet scanning a given point to generate the color-flow data. Such means should also not interfere with the resolution of image data which may be generated concurrently with the color-flow data.
Another problem experienced with existing ultrasonic scanning systems is that, while such systems can be easily focused for a point at a particular depth, it is difficult to dynamically focus the system to remain in focus as the transmitted scan lines move deeper into the body, resulting in echo signals being received from successively deeper points. A particular problem in this regard is the delay line which may be utilized to sum the received echo signals from the transducer elements. The delay line is required because the echo wave front does not strike all of the transducer elements at the same time, resulting in the echo signals from the various transducer elements being out of synchronization. The received echo signals are applied to taps on the delay line in a manner such as to compensate for the variable times at which the signals are received, resulting in the summing of comparable points sensed by each of the transducer elements. However, as the echo signals come from deeper in the body, and thus further from the transducer elements, the differences in time at which the signals are received at the elements decreases. If the delays between taps on the delay line to which the received signals are applied remain constant, this results in the image being out of focus for the deeper points. However, if an attempt is made to switch the delay between taps in the middle of a scan line, the resulting transient may cause noise, and thus distortion of the image. Heretofore, there has been no acceptable solution to the problem of dynamically focusing the delay line. Thus, the delays are either selected for a particular depth with the image being slightly out of focus at other depths, or an average value is selected for the delays which results in the images being increasingly out of focus at near and far depths. A need therefore exists for a technique to permit the dynamic focussing of the summing delay line used in ultrasonic delay line systems without resulting in switching transient noise.
In addition to the specific problems identified above, other situations arise in ultrasonic transducer systems where, in response to selected input conditions, it may be desirable to alter the delays between taps or otherwise reconfigure the delay line, such as by converting it into two parallel lines rather than a single serial line. It would therefore be desirable if the delay line utilized in such systems could be designed so as to be reconfigurable in response to selected inputs or detected conditions, such reconfiguring occuring simply and inexpensively and with the addition of a minimum amount of circuitry.